As described in DE-AS No. 1 146 254, when polymerization of an unsaturated monomer such as a methacrylate ester is initiated at room temperature and rapidly proceeded by the use of a multi-component system of a polymerization initiator and an accelerator (hereinafter referred to as "initiator system"), a process comprising an independent addition and mixing of each component of the initiator system with the monomer has a problem in that the components are hardly mixed homogeneously in a short time and the polymerization reaction cannot be sufficiently effected. In addition, a process comprising premixing each component of the initiator system and adding the mixture to the monomer has a problem such that, depending on a combination of the components, a reaction among the premixed components occurs so that the components are degraded in a short time.
The above DE-AS describes an initiator system and a manner for adding it which do not suffer from the above problems and are used in a process in which polymerization of the unsaturated monomer such as the methacrylate ester is initiated at room temperature and conducted comparatively rapidly.
The initiator system proposed in the above DE-AS is one comprising an alkyl acyl peroxide, a specific compound containing a halogen atom, a sulfur-containing compound, and as an optional component a heavy metal containing compound. The addition of the initiator system to the monomer is carried out by adding a solution of the alkyl acyl peroxide and the specific compound containing the halogen atom in an inert solvent to a system in which the monomer, the sulfur-containing compound, and optionally the heavy metal containing compound are premixed.